Agriculture Reference
In-Depth Information
Family PHYLLOXERIDAE
Viteus vitifoliae
(Fitch)
Grape phylloxera
tions are of particular significance on mature,
unsprayed apple trees and pear trees. The shoots
and branches become encrusted with scales and
heavily infested hosts are weakened.
This notorious pest was introduced into Europe
from North America in the mid-nineteenth cen-
tury. The pest destroys the young roots of grape
vines and also produces extensive callusing of
the older roots. European grape vines are espe-
cially susceptible to attack and their complete
destruction is possible unless they are grafted
onto phylloxera-resistant rootstock. The pest can
also produce greenish or reddish, wart-like galls
on the underside of leaves (cf. galls formed by
the grape erineum mite,
Colomerus vitis,
p. 258)
but these are of little or no direct significance.
BIOLOGY
Eggs overwinter, sheltered beneath the protec-
tive maternal scale, and hatch in late May or
early June. The first-instar nymphs ('crawlers')
are relatively active and crawl over the host plant
for a few days before becoming sedentary. They
then insert their mouthparts and begin to feed,
usually on the shoots and branches but occasion-
ally on leaves and developing fruits. They pass
through three nymphal instars and reach the
adult stage in late July. Eggs are laid from Au-
gust onwards; the adults then die. There is one
generation annually. This insect usually breeds
parthenogenetically but some races reproduce
sexually, with males appearing in early August.
BIOLOGY
In Europe, this pest persists as radicicolae (which
breed asexually on the roots of grape vines),
each female laying eggs which normally give rise
to nymphs that develop into further radicicolae.
There are several such generations annually.
Occasionally, eggs laid by radicicolae produce
nymphs that, instead of becoming radicicolae,
invade the aerial parts of the plant and develop
into gallicolae. These gallicolae feed and breed
within distinctive leaf galls. Nymphs emerging
from their eggs either continue to develop in leaf
galls as gallicolae or disperse to the roots, where
they will develop into radicicolae. Although
there is a sexual phase in the life-cycle, this very
rarely occurs in Europe.
DESCRIPTION
Adult female scale
2-3 mm long, grey to
yellowish-brown, elongate but mussel-shaped
(see Fig. 45a).
Adult female
2.5 mm long, body
subelongate, with a distinct pygidium (see Fig.
45b).
First-lnstar nymph
pale yellowish-brown,
oval.
Family COCCIDAE (soft scales)
Coccus hesperidum
L.
Brown soft scale
This generally common, polyphagous scale in-
sect is often present on glasshouse-grown
ornamentals and house plants; in favourable ar-
eas, including southern England, infestations
also occur outdoors. Although attacks are usu-
ally unimportant, the quality of host plants in
commercial nurseries may be affected adversely
by the presence of the scales, sticky honeydew
and sooty moulds.
DESCRIPTION
Asexual (apterous) adult female
1.4 mm long,
yellow to yellowish-green and plump-
bodied.
Nymph
oval-bodied, whitish to pale
yellowish-green.
Family DIASPIDIDAE
(armoured scales)
Lepidosaphes ulmi
(L.)
Mussel scale
BIOLOGY
Under favourable conditions, this usually par-
thenogenetic species breeds continuously; it is
also viviparous, with mature females producing
about a thousand nymphs during a life-span of
This generally abundant scale insect is associated
with a wide range of trees and shrubs. Infesta-
